Sense Organs

Specialized organs consisting of sensory cells that respond to the external stimuli to convey impulses to the sensory system of the body are known to be sense organs.  

Sense organs play an important role in a variety of functions and help in perceiving our surroundings. These are an integral part of our bodies that enable us to sense the environment around us. Sense organs and their receptors trigger numerous stimuli that are then transmitted to the brain. A network of nerves and sense organs is associated with interpreting data in response to a special physical phenomenon. This is the way that decides our interaction and response to the environment.

So, how many sense organs do we have? We have five primary sensory organs and the sense organs names are:

• Ears

• Eyes

• Nose

• Tongue

• Skin

These classic five sensory organs help in perceiving sound, light, smell, taste, and touch, respectively. Receptors present in the sense organs can transmit a signal to a sensory nerve, and these are classified into two, namely- general receptors and special receptors. Special receptors have specialized sense organs that include eyes for vision, ears for hearing and balance, tongue for taste, and nose for the smell. General senses are all associated with the sense of touch and do not bear special sense organs. Touch or general receptors are found throughout the body (skin). Preparation of a sense organs chart will help understand better about sense organs and their functions.

Our Five Sense Organs

As discussed above, our 5 sense organs are capable of receiving and relaying sensory information to the brain. It’s necessary for an organism to perceive information with the help of sense organs. Below are the five sense organs and their functions described in detail.

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Ears- Sensory System for Hearing (Audioception)

Also known as the auditory sense organs, ears play an important role in hearing or perceiving sounds. After detecting sound waves or vibrations in the air, our auditory system helps us in hearing sounds. The ear is also important for our sense of balance (equilibrium) as it is known that the vestibular system, also known as the organ of balance, is found inside the inner ear. Three parts of the ear are namely-

• Outer Ear- It consists of the visible portion known as auricle or pinna, and a short external auditory canal (eardrum) enclosed by the tympanic membrane. The outer ear collects sound waves and makes these reach the tympanic membrane.

• Middle Ear- It is a narrow air-filled cavity in the temporal bone and surrounded by three tiny bones that include hammer (malleus), anvil (incus), and stirrup (stapes). Auditory ossicles are the name given to the combination of these bones.

• Inner Ear- Two functional units of the inner ear are the vestibular apparatus having vestibule and semicircular canals, and cochlea having sense organs of hearing. 

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Eyes- Sensory System for Vision (Ophthalmoception)

Eyes are sensitive to all light images; it collects data from an environment to send to your brain for processing. This light is converted into usable information by the brain enabling you to differentiate how bright, what colour, or how far the object is situated. The cornea and lens are the two layers of an eye through which the incoming light travels. The former layer is at the front of an eye, and the latter layer is situated right behind the pupil; both work in tandem focusing the light ray onto a spot on the retina (located at the back of an eye). After the light is focused on the retina, it triggers photoreceptors leading to generating visual cues. The two kinds of photoreceptors include the following:

• Rods: These are more sensitive to light as compared to the cones, however, they cannot detect colour. There are nearly 120 million rods in the retina.

• Cones: These can detect colour, the three types of cones can perceive different colours including red, green, and blue, that further combine to create the full range of colours. There are nearly 7 million cones in the retina. 

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Tongue- Sensory System for Taste (Gustaoception)

One of our sense organs is the tongue that helps in perceiving tastes and flavours due to the presence of taste buds. Papillae consist of these taste buds on the tongue and it helps in sensing different tastes. Nose and tongue, together are associated with discriminating flavours and work together to create a taste. The receptors present in the taste buds are called chemoreceptors functioning similar to that of the present in the nasal cavity. The difference lying here is that there are four different taste buds on the tongue to detect different tastes like sweet, bitter, sour, and salty. 

Nose- Sensory System for Smell (Olfacoception)

Known as an Olfactory organ, the nose helps us to perceive a variety of smells. It also plays a role in sensing taste and is a part of the body’s respiratory system. We inhale air through the nose and as it passes over olfactory cells (chemoreceptors), the brain recognizes and identifies different smells. Hairs in the nose called cilia, move back and forth to take out the mucus from the sinuses and back of the nose. 

Skin- Sensory System for Touch (Tactioception)

The largest sense organ of our body is Skin and it relates to the sense of touch known as tactioception. It is a flexible outer covering of the body that comprises hair follicles, nerves, nails, and glands. The three major functions of Skin are protection, sensation, and regulation. It consists of sensory nerve structures or receptors that detect surface temperature, pain, physical touch, and chemical stimuli. The three layers of the skin include the following:

• Epidermis- It is the outermost layer called keratinocytes that contain a protein called keratin. Melanocytes, Merkel cells and Langerhans cells are also present in this layer. It is further divided into multiple layers.

• Dermis- It is located beneath the epidermis and consists of papillae. It is responsible for making skin flexible and sturdy due to the presence of fat, collagen and fibers. It plays an essential role in supplying blood for new cell formation via blood vessels.

• Hypodermis- It is a subcutaneous layer made up of fat that provides energy and regulates temperature. It is highly beneficial for cushioning internal organs, bones, muscles, and protecting these from injuries.

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Other Sensory Organs

Besides the five sense organs and their functions discussed above, there are other sensory organs that aid us in perceiving different sensations. The following are the two other sensory systems that signal the brain for varied functions.

• Vestibular System- It signals the head position, spatial orientation, motor functions and motions. Maintaining body posture, body balance, stabilizing head and body, etc. are among the essential functions of the vestibular system.

• Proprioception System- It helps in making us aware of the joint position, consciously, or unconsciously. Some of the examples of the proprioception system include the balance on one leg, kicking the ball without looking at feet, and sensing the surface we are standing upon.

To conclude the article, we can say that sense organs are important for the survival of the species. We have learnt bout all the major five sense organs.